1. Technical Field
The present invention relates to a liquid ejecting head, such as an ink jet recording head, and a liquid ejecting apparatus and more particularly to a liquid ejecting head that is provided with a flow passage unit, which forms a continuous liquid flow passage extending from a common liquid chamber through pressure chambers to nozzle openings, and that is able to discharge liquid from the nozzle openings as liquid droplets, and a liquid ejecting apparatus.
2. Related Art
A liquid ejecting head that discharges liquid droplets from nozzle openings by generating pressure variation in the liquid contained in pressure chambers, for example, includes an ink jet recording head used for an image recording apparatus, such as a printer, a color material ejecting head used for manufacturing a color filter for a liquid crystal display, or the like, an electrode material ejecting head used for forming an electrode for an organic electro luminescence (EL) display, a field emission display (FED), or the like, and a bio-organic material ejecting head used for manufacturing a biochip, or the like.
The above described liquid ejecting heads have various types; however, for example, the ink jet recording head (hereinafter, referred to as recording head) used in an ink jet recording apparatus (hereinafter, simply referred to as printer) includes a flow passage unit that is formed by laminating a nozzle substrate, a flow passage substrate, and a diaphragm. The nozzle substrate has a plurality of nozzle openings formed therein. The flow passage substrate forms a flow passage portion, such as a pressure chamber space portion and a channel portion, which defines a continuous ink flow passage extending from a common ink chamber through pressure chambers to the nozzle openings. The diaphragm has diaphragm portions that face the pressure chambers and elastically deform in accordance with the action of pressure generating devices (for example, piezoelectric vibrators) (which may be regarded as a sealing plate that seals the opening of the flow passage substrate). Then, the flow passage unit is fixed to a head case that accommodates a vibrator unit. In the above recording head, the diaphragm portions are elastically deformed by the action of the piezoelectric vibrators that constitute the flow passage unit to thereby vary the volume of the pressure chambers. Thus, pressure variation is generated in the ink contained in the pressure chambers to thereby discharge ink droplets from the nozzle openings.
The head case is made of a plastic material that is more advantageous in terms of ease of formation, flexibility of shape and weight than a metal material. However, because a plastic material is generally lower in rigidity than a metal material, the head case may be compressively deformed due to the stress generated when the diaphragm portions are elastically deformed by the action of the piezoelectric vibrators. Particularly, compression deformation tends to occur at an open peripheral portion corresponding to the diaphragm portions in the head case. Then, there is a possibility that desired discharge characteristics of ink droplets cannot be obtained because of the occurrence of crosstalk due to the above deformation of the head case or deformation of the flow passage unit. Then, a reinforcing plate is laminated between the flow passage substrate and nozzle substrate of the flow passage unit to thereby enhance the rigidity of the head case and, as a result, the discharge characteristics of ink droplets have been attempted to improve (which is, for example, described in JP-A-6-99578).
However, when the reinforcing plate is laminated between the flow passage substrate and nozzle substrate of the flow passage unit, a flow passage also extends through the reinforcing plate and, therefore, the length of the flow passage increases. Thus, a nozzle side resistance and/or an inertance increase, so there is a problem that it becomes unsuitable for ink discharge with high response frequency or the discharge characteristics of the nozzle opening is not uniform.
In addition, as the size of the recording head increases, in the head case, the opening portion of an accommodation chamber for accommodating the vibrator unit increases. Then, as the size of the opening portion increases, the rigidity entirely decreases. Particularly, the rigidity at the center of the opening portion in the longitudinal direction is weaker than the rigidity at each end portion of the opening portion in the longitudinal direction. Therefore, there occurs a difference in the amount of displacement, or the like, between the diaphragm portions arranged at each end portion of the opening portion and the diaphragm portions arranged at the center of the opening portion. Thus, there has been a problem that uneven discharge characteristics occur among the nozzle openings.